I want to figure out the difference between Xtool X100 Pad2 and EZ500.And to see how many Volkswagen cars are able to Pad2?

Answer to their difference:

1.VAG VW 4th 5th IMMO key programming (+& -)

XTOOL X100 PAD2 FULL Set can program VAG VW 4th 5th IMMO key, here a post on how to do: http://blog.xtooleshop.com/xtool-x100-pad-2-full-set-program-vag-vw-4th-5th-immo-key/

If your XTOOL X100 PAD2 without VAG 4th 5th IMMO key programming function, order a KC100 adapter, this is a little bit expensive, maybe you contact the seller they would give you discount especially when they promote.

2.4 system diagnosis VS full system diagnosis

You can see XTOOL X100 PAD2 have four systems diagnosis (Engine, Brakes, Central Electrics, Airbag), no full-system diagnosis. And XTOOL EZ500 have full-system diagnosis option. EZ500 is powerful with many functions and vehicle coverage, I already prepare a post on all EZ500 functions and testable car models & year: